The present invention relates to switches utilizing a bowed spring as an actuating mechanism.
In U.S. Pat. No. 5,446,252, issued Aug. 29, 1995, a switch assembly was disclosed utilizing a flat spring actuating mechanism formed from a bowed piece of spring steel for engaging the plunger of a plunger type switch. An improved, water resistant version is disclosed in U.S. Pat. No. 6,982,392. Commercial embodiments of these switch assemblies have been sold as the THINSWITCH® limit switch by Burger & Brown Engineering, Inc. The flat spring actuating mechanism is particularly well adapted for use with plunger type switches that are often referred to as micro-switches. In such micro-switches, the length or height of the switch (the dimension of the switch extending along the axis of the plunger) is generally considerably greater than the thickness of the switch. To minimize the thickness of the switch assembly, the micro switch is mounted on its side in a housing and the bowed spring is positioned in the housing so a first end abuts against the plunger with the middle portion of the spring extending up through a hole or slot in the housing. Pressing down on the middle portion of the spring causes the ends of the spring to move outward, driving the first end against the plunger and advancing the plunger a sufficient distance to change the condition of the switch. Upon removal of the external force acting on the spring, the spring returns to its original bowed state such that the first end of the spring advances away from the plunger and the plunger is allowed to move to the extended position changing the switch back to its original condition.
The switch assembly utilizing the flat spring actuating mechanism disclosed in U.S. Pat. No. 5,446,252 is particularly well adapted for use as a position sensing switch to sense when one portion of a piece of equipment is or is not positioned in a designated position. For example, a mold assembly for an injection mold utilizes ejector pins for ejecting the molded part out of the mold when mold halves of the mold assembly are separated. The ejector pins are typically mounted on an ejector plate that moves between extended and retracted positions relative to a respective mold half to advance the ejector pins into and out of the mold cavity formed in the mold half for ejecting the molded part from the mold assembly. It is important to ensure that the ejector pins are withdrawn from extending into the mold cavity before the two mold halves are brought together in the subsequent cycle for molding the next part. If the pins are not retracted they may be damaged upon closing of the mold.
The switch assembly of U.S. Pat. No. 5,446,252 is particularly well adapted for confirming that the ejector plate, and therefore the ejector pins, are fully retracted before closing the mold. When the ejector plate is fully retracted, low profile, cylindrical stops on an outer surface of the ejector plate abut against an interior wall of the mold assembly and more specifically an interior wall of the ejector housing. Alternatively, the stops may be mounted on the interior wall of the ejector housing. In most molds made in the United States, the height of the cylindrical stops is typically 3/16 of an inch or 0.1875 inches.
A preferred micro switch utilized in the THINSWITCH limit switch for the ejector plate application as described, is a subminiature basic switch No. 91SX39-T sold by the Micro Switch Division of Honeywell. This switch has a thickness of approximately 0.156 inches and is believed to be the thinnest micro switch having sufficient mechanical life and electrical rating for its intended application. At 0.156 inches, the 91SX39-T switch can be utilized in the switch assembly and fit within the gap of 0.1875 inches created by the stops on the ejector plate.
However, in molds manufactured in Europe and Asia, the stops are often only 3 millimeters (mm) or 0.118 inches tall, which is less than the thickness of the smallest commercially available micro-switch having sufficient life cycle and electrical rating for use as part of a limit switch assembly for mold ejection assemblies. Therefore, there remains a need for an even thinner yet rugged position sensing switch assembly which is particularly well adapted for industrial applications including use in association with injection molding machines.
There also remains a need for a better system for attaching the switch assembly of the type disclosed in U.S. Pat. No. 5,446,252 to an ejector housing of a mold assembly. Currently, the mold must be disassembled to provide sufficient access to the ejector housing to allow holes to be tapped therein so that the switch assembly housing may be screwed to the ejector housing.